Sir Ian McKellen is "going to marry" Patrick Stewart.
The 73-year-old actor will officiate at the ceremony between his friend and X-Men costar and his fiancee, jazz singer Sunny Ozell, when they tie the knot in Masachusetts.
He said: "I'm going to marry Patrick [Stewart]. I am going to officiate at his wedding.
"In Massachusetts, in the middle of America somewhere, you get a friend along, and I read out the words, and Sunny and Patrick will then be married."
The British actor revealed it won't be the first time he has officiated at such a service.
Speaking on an upcoming episode of The Jonathan Ross Show, he added: "I've done it once before with two guys having a civil partnership. I was crying my eyes out.
"I wore a white gown which I bought in India. You mustn't upstage the bride."
Massachusetts' Secretary of Commonwealth offers a service that allows a family friend or relative to perform a couple's wedding ceremony for a fee of R225.
Stewart (72) and Ozell (35) have been dating since 2009.