How would you react if a famous face showed up at your wedding ? Well, quite a few lucky couples got to find out when stars like Brad Pitt, Robert Pattinson , and even Queen Elizabeth II made surprise appearances at their nuptials over the years, and Beyoncé is the latest star to make someone's big day even bigger by unexpectedly crashing their ceremony. Keep reading to see which A-listers have popped up during regular folks' big days.
During a vacation with her husband Jay Z in Portofino, Italy, in September, Beyoncé inadvertently crashed an unsuspecting couple's wedding  when she wandered into a local church. Clad in a bikini, sheer skirt, and straw hat, the singer happily posed for photos with the beaming bride, who seemed more than happy about the interruption.
Serena WilliamsSource: Getty / Dave Lee 
In May 2014, Serena Williams surprised a couple getting married on the sand  in Miami. Since the bride and groom were out on the beach, Serena swung by while still wearing her swimsuit — a leopard, off-the-shoulder one-piece. The tennis star posed for photos with guests and later uploaded snaps of her own to Instagram , calling herself a "bikini wedding  crasher."
Conan O'Brien showed up at the Atlanta wedding  between Wes and Victoria Hoffman back in April 2013 after he had been jokingly invited by a fellow partier on Twitter. Much to everyone's surprise, the late-night host showed up at the reception and took photos with all the guests.
Brad Pitt sort of crashed Abi and Daniel Lingwood's wedding  September 2013 when he showed up at a hotel bar in Buckinghamshire, England, on Friday and ran into the newlyweds. The bride thought her husband was joking when he spotted him in the hotel, and the two couldn't pass up the opportunity to ask him for a photo. The actor was filming Fury nearby.
Justin Bieber  and Selena Gomez
Fans got a two-for-one treat when Justin Bieber and Selena Gomez crashed a beach wedding in Malibu  back in July 2011. According to Justin, he heard his song "One Less Lonely Girl" playing at the reception while going on a stroll with his then-girlfriend, so the two decided to make an appearance at the party.
John Travolta got a last-minute invite to attend a couple's wedding  after he ran into them the day before the nuptials in Georgia last Summer. To the bride and groom's surprise, John actually showed up and posed for photos with the entire wedding party. This wasn't the first wedding that John crashed  — he revealed several years ago that he and Robin Williams  decided to pop by a random wedding in 1977 in Santa Barbara.
Robert Pattinson and Katy Perry
Robert Pattinson and Katy Perry made one bride's day when they subtly crashed her wedding  in Montecito, CA, in May 2013. The two friends reportedly watched the ceremony from a distance after stumbling on the wedding during a walk. The two stars didn't mingle with the guests, but according to family members, they were "the talk of the wedding."
Queen Elizabeth II
While not technically a wedding crasher , no one was expecting Queen Elizabeth II to show up at the wedding between John and Frances Canning in Manchester, England, in March 2012. According to the couple, they had jokingly sent an invitation to Buckingham Palace and were stunned when the royal actually made an appearance at their ceremony. She met briefly with the couple and then continued with her work schedule for the day.
Bill Clinton made a surprise appearance at an Irish-American couple's wedding  in Cork, Ireland, in June 2012. The former president was staying at the same resort where the couple were holding their nuptials, so he decided to stroll over and introduce himself.
LeBron James crashed Shaun and Jamie Kolnick's wedding  in Miami in June 2012. The Miami Heat basketball player happened to be doing an interview at the Ritz-Carlton Coconut Grove, right where the couple was getting hitched.
Want more of stars at weddings? Be sure to check out your favorite celebrities when they were actually invited wedding guests  and get tons of wedding inspiration here .