"Bachelorette" Star Ryan Sutter Runs Boston Marathon!

Ryan Sutter was looking really good today in Boston ... for a really good cause!

Ryan's "Bachelorette" star wife Trista shared the above photo of her hot hubby just moments after he completed the Boston Marathon.

In just 3 hours and 36 minutes, Sutter completed the 26.2 mile haul -- which he ran in honor of good friend Ethan Zohn.

Zohn, who won the third season of "Survivor," had planned on running this year -- but was sidelined after undergoing stem-cell transplant to treat Hodgkin's Lymphoma.

Sutter reportedly did the marathon in support of Grassroot Soccer, a charity Zohn co-founded.

With temperatures in the 80s, it was one of the hottest marathons to date -- something Sutter tweeted about after the run.

The race was so hot I pretty much ran naked. Just my @2XU_USA shorts and my @nike shoes. Took about 50 sprinkler showers to survive!

— Ryan Sutter (@ryansutter) April 16, 2012