Deploying to Digital Ocean from Bitbucket - Permission denied (publickey) error

OK, I found the solution, I will add it here so that someone might find it useful.

I fixed the problem my creating a SSH key in Digital Ocean and adding it to Bitbucket.

Following are the steps

• create a SSH key in Digital Ocean
• add that SSH key as a Digital Ocean SSH key
• add the same key to Bitbucket deployment key (https://bitbucket.org/<user>/<project>/admin/deploy-keys)